Scientists have unveiled the latest prototype of a car that "drives itself" with the help of a tablet computer.

Acting like a plane on auto-pilot, it is designed to take over from humans in slow-moving heavy traffic or on a familiar route, such as a school run.

It is activated using an iPad on the dashboard - by tapping on a prompt, the driver can make the car's onboard computer take the wheel.

Robotcar, which is being developed by Oxford University and Nissan at Begbroke Science Park in Oxfordshire, uses a combination of external sensors and computer power to calculate the correct direction and speed.

Professor Paul Newman told Sky News: "Instead of imagining some cars driving themselves all of the time we should imagine a time when all cars can drive themselves some of the time.

"The sort of very low-cost, low-footprint autonomy we are developing is what's needed for everyday use.

Scientists hope something like this will soon become a mainstream car

"It's easy to imagine that this kind of technology could be in a car you will buy."

Google has been testing a fleet of computer-controlled cars in the US for years.

And smart technology is already a part of new cars produced around the world, with motion sensors, guided parking and cruise control.

The technology used in Robotcar currently adds £5,000 to the cost of a typical vehicle, but researchers are confident prices will fall with mass production.

However, motoring writer Mike Rutherford cautioned that insurers might be reluctant to provide coverage for such vehicles.

"It's difficult enough to get cars insured when you're a driver with a decent record and you have no history of crashes or endorsements," he said.

"Imagine contacting a comparison website and trying to explain that you don't actually want to drive it, you just want to ride as a passenger in it and the car drives itself."